Faulty tach operation

[HighOctane]

Hydrostream vector with tachometer problems. Turn key to half on and tach sets itself up and back to zero, upon complete cranking and running boat, it sits at zero. At times it will raise and lower like its trying to read. So I know it's got power to it, fuse is good etc etc. I think the question is whether or not it's reader line is connected properly. What to look for??

[daytrader]

What kind of motor?

[HighOctane]

89' Merc 200 rebuilt to 260. All old school, no EFI. Simple quicksilver side control. Wires on back of tach seem to be connected properly, and if im correct this wiring harness continues to the control? It's connected as well, mild corrosion from weather.

[daytrader]

Is that a standard 16 amp stator with rectifier system. I have a vector also, when my tach didnt work it was the rectifier. 87 v6 merc, 16 amp system
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[HighOctane]

Ah, that makes sense. Yea I believe its 16 amp, so when yours did not work did it at least zero in or did it flat out not respond to key turn?

[flabum1017]

That could be a number of things, first clean the connections at the control box where it plugs in, then go back to the motor and check the connections at the main harness connection, the big black cannon plug.... you can spread the pins a little to make it get a better conection there. If those things don't work then you will need to test the stator and rectifiers.

There should be 3 - 6 volts on the tachometer sensor wire, if you have that at the tach, it might be a bad tach.

[Go Time]

What are you using for the retifier/regulator with you 16 amp system? could be the rectifer.

[HighOctane]

Thanks so much for the replies, will be testing rectifier soon and post results! I found a site that shows which specific poles to test at each time, and yes UNSCREW the terminals while testing for accurate results, haha. Just makes me wonder if rectifier is bad, how does the battery stay well charged, seems to be doing it's other jobs well. Maybe different poles do different jobs huh

[Go Time]

Some engines with 16 amp stators are retro fitted with the new style 16/20 amp regulator/recifier. These will continue to charge the battery but the tach signal (gray lead) can stop working.

[HighOctane]

U guys are too smart, seems to be recrifier. No continuity in either of two tests. (Have a Merc manual now) . Now to find another rectifier... Are most the same? When I look on eBay there are different ones from the same company all ranging in year model of Merc. They all look the same, do they forgo different voltages?

[daytrader]

Try connecting the tach wire at the motor to one of the 2 yellow leads that u took off the rectifier (leave wires disconnected from rectifier) with motor running, tach should work if its good. Either yellow wire should work. If u want put a test lite to the yellow wires and it should light up when running. Yellow wires are the charge coil wires giving tach its signal, u can just hold the tach wire to the yellow lead. If the test lite doesnbt lite up you might have a problem with the stator. Is this an old tach?